Method of and means for generating electrical energy



y 1951 E. G. LINDER 2,552,050

METHOD OF AND MEANS FOR GENERATING ELECTRICAL ENERGY Filed June 25, 19462 Sheets-Sheet} INVENTOR. Lin

y 1951 E. .G. LINDER 2,552,050

METHOD OF AND MEANS FOR GENERATING ELECTRICAL ENERGY Filed June 25, 19462 Sheets-Sheet 2 INSULATION LOAD Z #vsumnom IN VEN TOR. Ernes26l1nderATTORNEY Patented May 8, 1951 METHOD OF AND MEANS FOR GENERATINGELECTRICAL ENERGY Ernest G. Linder, Princeton, N. J., assignor to RadioCorporation of America, a corporation of Delaware Application June 25,1946, Serial No. 679,085

8 Claims.

This invention relates generally to the generation of electrical energyand more particularly to unique methods of and means for deriving andutilizin the electrical energy of nuclear reactions.

The enormous magnitudes of energy provided by certain nuclear reactionsof some radioactive substances provide a tremendous field for thedevelopment of new sources of electrical energy. Since radioactiveradiations (energy) are largely electrical in nature, it is desirablethat such electrical energy be converted directlyto electrical energy ofusable form. The alpha-particle and beta-particle emissions from certainradioactive substances comprise positively or negatively chargedparticle rays, respectively, having energies which vary from low valuesto several million electron volts. Other charged and uncharged particlesalso may be emitted. For example, alpha-ray emission comprisespositively charged particles having energies varying from zero to theorder of ten million electron: volts, while beta-particle emissioncomprises negatively charged particles having energies varying from lowvalues to the order of three million electron volts. Nuclear reactionsare known to provide either alpha-particle emission, beta-particleemission, or a combination of alpha-particle and beta-particle-emission,as. well as other types of charged and unchargedparticles not generallyso well known. The direct utilization of the high electrical potentialswhich may be derived from such charged particles provides, in the casesin which the particle emission is charged, much more convenient andefiicient utilization of nuclear energy than previously proposed systemswherein the nuclear energy is converted to thermal energy, the thermalconverted to mechanical energy, and the mechanical energy then convertedto electrical energy in a usable form. Also, the direct utilization ofthe electrical energy of nuclear reactions may be much more readilycontrolled by electrical methods than may the conversion of nuclearenergy to thermal energy.

The instant invention is an improvement over the methods and systemsdescribed and claimed in applicants copending U. S. application, SerialNo. 679,081, filed June 25, 1946, now Patent No. 2,517,120, August 1,1950, which contemplates the use of collector electrodes for collectingthe charged particle rays from a radioactive source, and means forapplying the resultant unidirectional potential between the source andcollector electrodes to a load; The improvement comprising the instantinvention includes unique inethods of and means for segregating andutilizing separately the electrical properties of alphaparticle andbeta-particle or other charged particle emission from radioactivematerials to generate separate voltages and thence combining saidvoltages. It utilizes the distinguishing characteristics of differencesin charge, polarity, mass, velocity and penetration of diiierent typesof such particles.

Among the objects of the invention are to provide improved methods ofand means for gen-- erating electrical energy in response to nuclearreactions. Another object is to provide improved methods or" and meansfor utilizing the electrical energy in nuclear reactions for generatinghigh unidirectional potentials. A further object is to provide improvedmethods of and means for utili'zing the electrical energy of nuclearreactions for generating alternating potentials. An additional object isto provide improved methods of and means for utilizing atomic energy forgenerating electrical energy. A still further object of the invention isto provide improved methods of and means for utilizing radioactivematerials as sources of electrical energy.

Another object of the invention is to provide improved methods of andmeans for converting atomic energy directly to electrical energy incommercially usable forms. A still further object is to provide improvedmethods of and means for segregating and separately utilizing theelectrical energy of alpha-ray and beta-ray or other charged particleemissions of radioactive materials for generating electrical energy.

Other objects of the invention include improved methods of and means forconverting the electrical energy of nuclear reactions of radioactivematerials to high frequency electrical energy. A still further object isto provide improved methods of and means for utilizing and combinin thealpha-ray and beta-ray electrical potentials of nuclear reactions fordirectly deriving electrical energy in commercially usable form;

The various embodiments and features of the invention will be describedin detail hereinafter by reference to the accompanying drawings of whichFigure 1 is a schematic disgram of a basic embodiment of the inventionaccording to said copending application and including a simpleunidirectionall voltage generator; Figure 2 is a cross-sectional diagramof a modification of said basic embodiment of the invention; Figure 3'is a cross-sectional schematic diagram of another modification of saidbasic embodiment of the invention; and Figures 4 and 5 arecross-sectional,

. source terminal 9.

partially-schematic diagrams of first and second embodiments of theinstant invention each utilizing combinations of alpha-ray and beta-rayemission for generating electrical energy. Similar reference charactersare applied to similar elements throughout the drawings.

High-ololtage D.-C. generators Referring to the drawings, Figure 1illustrates the simplest form of the basic embodiment of the inventiondisclosed and claimed in said copending application comprising aunidirectional high voltage generator I. The generator I includes asource 3 of alpha-rays or beta-rays derived from a quantity ofradioactive material. A suitable alpha-ray radioactive source maycomprise, for example, a quantity of polonium (84Po Likewise, a suitablebeta-ray source may comprise a suitable quantity of radioactivephosphorus (15P Radioactive phosphorus is a pure beta-ray emitter whichbecomes stable after emission. It is thus suitable for use as anelectronic power source since it emits no gaseous reaction products and,therefore, it is suitable for vacuum applications. One gram of thismaterial occupies about .5 cubic centimeter and will emit about 2milliamperes of electron current. The maximum energy of the beta rays isof the order of 1.7 million electron volts, but only a small fraction ofthe electron current would be available at such a high voltage. However,about 1 milliampere of current would be emitted at one megavolt. Sincethe average energy of emission would be about 1 million electron volts,the total electrical energ or power emitted would be about 2 kilowatts.The half-life period of radioactive phosphorus (151 is about 14 days,and the current and power would decrease exponentially to one-half theirinitial values in that time.

The radioactive source 3 is surrounded, for example, by a sphericalhighly evacuated conductive collector electrode 5 having an apertureinsulator l therein for a suitably insulated terminal 9 for theradioactive source 3. A load II is connected between the collectorelectrode 5 and the If desired, the collector electrode 5 may begrounded.

In operation, and in the absence of a load, beta particles (electrons)emitted by the radioactive source 3 travel to the collector electrode 5and charge it negatively as indicated by the dash line arrow I3. Thecharge upon the collector electrode is negative with respect to thesource 3 and increases until the potential of the collector electrode issufficiently high to repel additional electrons arriving from the source3 is shown by the dash line arrow l5. If it is assumed that theradioactive source 3 emits 1 megavolt electrons (beta rays), thepotential of the collector electrode 5 would reach one megavolt andwould be negative with respect to the radioactive source. If a load isconnected between the collector electrode and the source terminal, acurrent will flow through the load and power will :be dissipatedtherein. Thus the radioactive energy emitted in the beta rays may beemployed directly in its original electrical form to provide electricalenergy.

Known beta-ray emitters provide electrons having energies from almostzero to 3 million electron volts. Known alpha-ra emitters providepositively charged alpha particles having energies from about zero tothe order of 10 million electron volts. If desired an alpha-particlesourc may be employed instead of a beta particle source, in which casethe collector electrode 5 will be charged positively until it reaches apotential sufficiently high to repel additional alpha particles. In sucha modification Of the invention, the collector electrode 5 becomes thepositive terminal and the radioactive source 3 the negative terminal ofthe generator. Obviously other types of charged particles may beutilized.

The electric current produced by any source of charged particles is1,edt (1) where n is the number of particles emitted, t is the time inseconds, and therefore dn/dt is the rate of particle emission, and e isthe electrical charge per particle. If each particle carries more thanone electronc charge, 6 must be replaced by e, where ,u. is the numberof charges.

For a radioactive substance (see Pollard and Davidson, Applied NuclearPhysics, p. where is the decay constant The number of atoms contained ina substance of mass M and atomic weight A is where m is the mass of thehydrogen atom. Thus O.693 M611. m At (6) This relation may be expressedin amperes per gram for a predetermined quantity of a radioactivesubstance wherein c=1.59 x 10- coulombs, M 1 gram, m =1.66 10 grams, andt 8.64 10 T where T is the half life in days. Therefore,

If the radioactive source is polonium, A=2l0 and T =140, :2, therefore 51 .8 microamps. gram The characteristics of the charged particleemitting substance determine not only the output voltage of thegenerator, but also determine its impedance. Thus, since alpha particlesgenerally have a very uniform energy, the generated voltage would remainsubstantially constant until all the remaining current was drawn,whereupon the Voltage would decrease rapidly. Thus, with analpha-particle emitter, the generator would have a low effectiveinternal impedance. In contradistinction thereto, beta particles areusually emitted over a wide energy range which may vary from a very lowvalue to several million electron volts. Consequently, when current isdrawn from the generator to a load, the load voltage would immediatelydrop to a much lower value than the no load maximum, as ischaracteristic of all generators having high internal impedance. Theactual variation of load voltage with current would depend upon theparticular characteristics of the beta-ray emitting material. In generalthe available power depends upon the quantity of radioactive materialemployed and upon its rate of particle emission. Materials. which emitat high rates have short operating life, while materials emitting at lowrates have relatively longer operating lives. A D.C. generator of thetype described has particular application for systems requiring highvoltage and low power capacity sinc in such instances only a relativelysmall amount of radioactive material is required for the alphaorbeta-ray source.

For generators providing relatively large power values, cooling of thecharged particle source may be necessary or desirable since the sourceis bombarded and heated by the returning charged particles which arereflected by the charged collector electrode. Also the collectorelectrode is heated by the charged particles which it'collects. A simplesystem for cooling the charged particle emitter is shown in saidcopending application wherein the charged particle source 3 comprises arelatively thin shell of radioactive material into which air or waterunder pressure may be forced for cooling purposes. If desired, thecollector electrode may be cooled by air blasts.

Secondary electron suppression The principal limitations onthepotentials which may be attained by the device described heretofore isdueto leakage currents. Some of the leakage currents are due to theinherent limitations of insulating materials and the proportions thereofas determined by the proportions of the generator unit. Insulatorleakage currents may be reducedto negligible values by employinginsulator materials and shapes commonly used in high voltage work.Another serious source of leakage currents arises from the nature ofradioactive radiations themselves.

Referring again to Figure l of the drawings, beta rays striking thecollector electrode 5 will cause secondary electron emission therefrom.

Such secondary electrons will be attracted toward the radioactive source3 which is positively charged with respect to the collector electrode 5,and thus will tend to neutralize the positive charge on the radioactivesource and hence decrease the potential difierence between the source 3and the collector 5-. a

Referring to Figure 2, inorder to reduce the efiect of secondaryelectron emission from the collector electrode 5, a grid or thinmetallic shell H is introduced into the generator in a regionintermediate the source 3- and collector 5, and is maintained at acomparatively small negative potential with respect to the collectorelectrode 5 by a battery it. connected between. the. collector and gridelectrodes. The biasing potential may be of the order of 100 to 1000volts. As explained heretofore, this potential may be derived from aseparate radioactive D.-C. generator since the energy required ispractically negligible. The negatively biasing grid electrode i'isuppresses substantially all secondary electrons emitted by thecollector electrode 5 and thus permits the potentialsbetween theradioactive source 3 and 'the collector electrode 5 to build up to avalue determined by the velocity of emission of thebeta raysand the loadresistance, as described heretofore.

Alpha-particle; suppression.

A further source of'leakage wouldoccur in instances wherein theradioactive source- 3" emits Delta-particle suppression Referring toFigure 3, when an alpha-particle radioactive source is employed, leakagemay result due to 6 rays which are slow electrons which accompany theemission of alpha rays. Such 6 rays would be drawn to the collectorelectrode 5, which in this instance would be positively charged withrespect to the alpha emitting source 3, and would result in chargeneutralization on. the collector electrode. To decrease this effect, thealpha particle emitting source 3 may be surrounded by a grid 23 which ismaintained at. a comparatively low negative voltage with respect to thealpha-particle source 3. This voltage may be derived from an externalbattery 25 connected between the source 3 and the grid 23 or it may bederived from an auxiliary radioactive generator. The bias voltageapplied to the grid 23 should be sufficiently high to suppress andreflect back to the source substantially all 6 rays emitted by theradioactive source 3, but will have little. efiect upon the highlypositively charged alpha particles emitted by the source.

Controllable radioactive generators When employing. radioactivematerials (either natural or artificial) for the production ofelectricah energy, the radioactive emission will decay exponentially asa function of the type of radioactive material employed. The decay ofradioactive: emission will provide a corresponding decrease in the;energy. which may be derived from the. generator. This. decay isuncontrollable since the active material is consumed. Whether ornotpcwer. is derived from the generator.

By utilizing. a reaction or. series of reactions of the. proper types,it is. possible to providev a radioactive electric generator which will.consume. the. radioactive material and deliver electrical energy onlywhen desired. An example of suchareaction is asfollows:

' in any other manner and with any other structure'known' in the art;

' Following-is-a partial'list" of'alphaandbeta-r 7 ray emitters whichare suitable for high voltage generators of the types describedheretofore:

Energly, t Half-life i 911 Element million 9 days electron voltsALPHA-RAY EMITTERS l 25 10 Polonium (P0 4 Actinium (Ac 11. 2 5. 66Thorium X (Th X 3. 64 5. 65 Radio actinium (Rd A0 18. 9 5. 92

BETA-RAY EMITTE RS Phosphorus (P 14 1.7 Calcium (Ca 180 Scandium (S0 S526 Iron (Fe 47 Arsenic (As 16 1.1: Strontium (SI 55 l. .1 Antimony (Sbl. 69 l. 53 Tungsten (W 74 (l. 5

Combined alphaand beta-ray generators High voltage D.-C. generators maybe provided to utilize a radioactive emitter providing both positive andnegative charged particles (alpha and beta rays or other chargedparticles of both polarities and differing velocities and penetration).An emitter of both alpha and beta particles is radium (C). A mixture ofsubstances such as radioactive polonium and radioactive phosphorus alsomay be utilized. The polonium provides pure alpha ray emission, and theradioactive phosphorus provides pure beta-ray emission. Such mixturesare frequently preferable since the ratio of the number of alpha andbeta particles may be controlled.

Referring to Figure 4, a radioactive source 21 providing both alpha andbeta particle emission is supported by terminal 29 from a high voltageinsulator which also supports a spherical evacuated beta-ray collectorelectrode 33. A thin metallic alpha-ray collector electrode 35 isinterposed between the source 2'? and the betaray collector electrode33. The alpha-ray collector electrode should be of sufficiently thinmaterial to be substantially opaque to alpha rays while substantiallytransparent to beta rays, as explained heretofore by reference to thedevice illustrated in Figure 2. A terminal 31 supports the alpha-raycollector electrode 35 and is insulated by a second high voltageinsulator 39 from the beta-ray collector electrode 33.

In operation the alpha-ray collector electrode 35 becomes positivelycharged to the potential of the alpha rays, and the beta-ray collectorelectrode 33 becomes negatively charged to the potential of the betarays, both with respect to the source 21. The voltage which may beapplied to a load 4| thus is the sum of the magnitudes of the voltagesestablished on the electrodes 33 and 35.

It is essential for proper operation of the device that the rate ofarrival of alpha particles on the alpha-ray collector electrode 35exceed the rate of arrival of beta particles by direct capture and byreflection from the beta-ray collector electrode .0 33. Suitableproportions of alpha ray and beta ray radiation may be assured byproviding a suitable mixture of alpha-ray and beta-ray emissivesubstances in the radioactive source 21.

- Amore complex structure utilizing combined alpha-ray and beta-rayemission for generating high D.-C. voltages is shown in Figure 5 whereina combined alpha ray and beta ray emissive source 43 is in the form of ahollow shell which is insulated from and surrounded by an evacuatedspherical beta-ray collector electrode 45. A secondary electronsuppressor grid or thin shell 41 is interposed between the beta-raycollector electrode 45 and the radioactive source 43 to preventsecondary electron emission from the beta-ray collector electrode fromreaching and neutralizing the potential of the radioactive source 43. Analpha ray suppressor electrode 49 comprising a thin sheet of aluminum orother suitable material opaque to alpha-ray emission but substantiallytransparent to beta-ray emission surrounds the external surface of theradioactive source 43. Thus the voltage on the beta-ray collectorelectrode 45 with respect to the radioactive source 43 is substantiallydependent only upon beta-ray emission.

An alpha-ray collector electrode 5| is disposed at the center of thehollow radioactive emitter 43 and is insulated therefrom in any suitablemanner. A beta-ray suppressor grid 53, biased negatively with respect tothe radioactive source 43, is disposed between the alpha-ray collectorelectrode 5i and the radioactive source 43. The negative potential forthe beta-ray suppressor grid may be derived by means of a directconnection between said grid and the beta-ray collector electrode 45whereby said grid is self-biased by the beta-ra emission.

The voltage established upon the alpha-ray collector electrode 51 thusis dependent substantially only upon the alpha-ray emission from theradioactive source 43. The sum of the voltages developed upon thebeta-ray collector electrode 45 and the alpha-ray collector electrode 5|may be applied directly to a load 55.

One of the advantages of the more complex structure illustrated inFigure 5 over the simple combination alpha and beta ray generator ofFigure 4 is that undesirable reaction upon the alpha ray collectorelectrode due to reflected or secondarily emitted electrons from thebeta-ray collector electrode is substantially eliminated, thus reducingleakage currents. 'It should be understood that the relative positionsof the alpha-ray generator portion and the beta-ray generator portion ofthe device may be interchanged with respect to the radioactive source.The principles and techniquesof the instant invention also may beapplied to the'generation of alternating potentials including energy ofmicrowave frequency by proportioning the collector electrodes toresonate at the desired output frequency a disclosed and claimed inapplicants copending U. S. application, Serial No. 679,083, filed June25, 1946.

Thus the invention described and claimed hereing comprises uniquemethods of and means for generating unidirectional or alternatingpotentials by utilizing directly the electrical properties ofradioactive emission. Such generators may provide high or lowunidirectional potentials with relatively low or relatively high currentoutput, respectively; and alternating potentials including A.-C. energyof microwave frequency. Control and focusing potentials for said devicesmay be provided by auxiliary radioactive generators, or self-biasingarrangements may be employed. Combinations of both alphaor beta-rayemission may be segregated or utilized separately.

I claim as my invention:

1. The method of utilizing a source of radioactive material providingpositively-chargedparticle and negatively-charged-particle emission forgenerating electrical energy comprising segregating and collecting saidpositivelycharged-particle emission in a first region adjacent to saidsource to establish a first potential with respect to said source,collecting said negatively-charged-particle emission in a second regionadjacent to said source to establish a second potential with respect tosaid source, substantially preventing charged particle interactionbetween said regions, and combining said potentials.

2. Apparatus for generating electrical energy including a source ofradioactive material providing both alpha-particle and beta-particleemission, means disposed adjacently to and in cperative relation withsaid source for collecting said alpha-particle emission to establish apositive potential with respect to said source, second means disposedadjacently to and in operative relation with said source for collectingsaid betaparticle emission to establish a negative potential withrespect to said source, means for substantially preventingalpha-particle irradiation of said second means, and means for combiningsaid potentials.

3. Apparatus for generating electrical energy including a source ofradioactive material providing both alpha-particle and beta-particleemission, first means substantially transparent to beta-particleemission and substantially opaque to alpha-particle emission surroundingsaid source for collecting said alpha-particle emission to establish apositive potential with respect to said source, second means surroundingsaid source and said first means for collecting said beta-particleemission transmitted through said first means to establish a negativepotential with respect to said source, and means for combining saidpotentials.

4. Apparatus for generating electrical energy including a source ofradioactive material providing both alpha-particle and beta-particleemission, first means substantially transparent to beta-particleemission and substantially opaque to alpha-particle emission surroundingsaid source, second means surrounding said source for collecting saidbeta-particle emission transmitted through said first means to establisha negative potential with respect to said source, third means inoperative relation with said source for collecting substantially onlysaid alpha-particle emission to establish a positive potential withrespect to said source, and means for combining said potentials.

5. Apparatus for generating electrical energy including a hollow bodysource of radioactive material providing both alpha-particle andbetaparticle emission, first screen electrode means substantiallytransparent to beta-particle emission and substantially opaque toalpha-particle emission surrounding said source, second meanssurrounding said source and said first means for collecting saidbeta-particle emission to establish a negative potential with respect tosaid source, a secondary-electron-suppressor electrode disposed betweensaid first and second means for preventing secondary-electron emissionfrom said second means from reaching said source, third means disposedWithin said hollow source for collecting substantially onlyalpha-particle emission to establish a positive potential with respectto said source, a beta-particle suppressor electrode disposed betweensaid third means and said source for substantially preventingbetaparticles from reaching said third means, and connections to saidsecond and third means for combining said potentials.

6. The method of utilizing a source of radioactive material providingpos'itively-charged-particle and negatively-charged-particle emissionfor generating electrical energy comprising segregating said chargedparticles as a function of their penetrating characteristics in aretarding medium, collecting said positively-charged-particle emissionin a first region adjacent to said source to establish a first potentialwith respect to said source, collecting said negatively-chargedparticleemission in a second region adjacent to said source to establish asecond potential with respect to said source, and combining saidpotentials.

7. The method of utilizing a source of radioactive material providingpositively-charged-particle and negatively-charged-particle emission forgenerating electrical energy comprising segregating saidpositively-charge-particles as a function of their penetratingcharacteristics in a retarding medium, collecting saidpositivelycharged-particle emission in a first region adjacent to saidsource to establish a first potential with respect to said source,segregating said negatively-charged-particles as a function of theirpenetrating characteristics in said retarding medium, collecting saidnegatively-charged-particle emission in a second region adjacent to saidsource to establish a second potential with respect to said source, andcombining said potentials.

8. The method of utilizing a source of radioactive material providingpositively-charged-particle and negatively-charged-particle emission forgenerating electrical energy comprising segregating said chargedparticles as a function of their penetrating characteristics in aretarding medium, collecting said positively-charged-particle emissionin a first region adjacent to said source to establish a first potentialwith respect to said source, collecting said negatively-charged-particleemission in a second region adjacent to said source to establish asecond potential with respect to said source, and utilizing saidpotentials.

ERNEST G. LINDER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,964,738 McCreary July 3, 19342,032,545 McElrath Mar. 3, 1936 OTHER REFERENCES Physical Review, vol.69, June 15, 1946, page 666 (A. E. D),

